Typically, during semiconductor processing, a plasma etch process is utilized to remove or etch material along fine lines or within vias or contacts patterned on a semiconductor substrate. The plasma etch process generally involves positioning a semiconductor substrate with an overlying patterned, protective layer, for example a photoresist layer, into a processing chamber and etching exposed areas of the substrate through the pattern.
Once the substrate is positioned within the chamber, it is etched by introducing an ionizable, dissociative gas mixture into the chamber at a pre-specified flow rate, while adjusting a vacuum pump to achieve a processing pressure. Then, plasma is formed when a portion of the gas species is ionized by collisions with energetic electrons. The gas may be ionized by direct current, radio frequency, microwave energy, or other energy sources known to the art. The energetic electrons dissociate some of the gas species in the gas mixture to create reactant species suitable for the exposed-surface etch chemistry. Once the plasma is formed, exposed surfaces of the substrate are etched by the chemistry at a rate that varies as a function of plasma density, average electron energy, and other factors. The process is adjusted to achieve optimal conditions, including an appropriate concentration of desirable reactant and ion populations to more selectively act upon various desired features (e.g., trenches, vias, contacts, etc.) in the exposed regions of substrate. The exposed regions of the substrate where etching is required are typically formed of materials such as silicon dioxide (SiO2), poly-silicon and silicon nitride, for example.
Dissociative attachment, in forming the ions during the exposed substrate etch process, prefers electron energy to be as low as possible. An example is where the chemistry is a Cl2+e− process yielding Cl+Cl−, the negative ions being extracted for etching. Moreover, it is highly desirable to accomplish this reaction in a spatial afterglow region of a plasma, to avoid periodic plasma density deficiencies and the resultant increased risk of damage from unmitigated electromagnetic waves reaching the substrate, for example in microwave plasma sources.
While plasma etching has proven to be generally effective, process efficiency may be negatively impacted by a variety of factors. For example, undesirably high average electron energies (Te) tend to impede ion formation, and thus results in reduced dissociative attachment at the substrate. Attempts to attenuate the negative effects noted above have included the introduction of Multi Pole Magnet (MPM) assemblies, for example as described in U.S. Pat. No. 5,595,627, entitled “Plasma Etching Method” and hereby expressly incorporated herein by reference. These configurations are not conducive to correcting magnetic irregularities by rotating the magnet assembly. Additionally, attempts to improve ion formation at the target substrate, have often necessitated more complex processing chemistries.
Therefore, an apparatus and method for uniformly applying low average electron energy plasma etch, to a substrate, is needed.